Effect of spontaneously generated coherence in controlling the optical bistability and multistability in a left-handed four-level atomic system

Abstract

In this paper, we theoretically investigated the influence of spontaneously generated coherence (SGC) on electromagnetic characteristics, and optical bistability (OB) and optical multistability (OM) of dense four-level atomic system. In the absence of the SGC effect, this atomic system exhibits left-handed property in one frequency detuning band of the probe field, while in the presence of the SGC effect it exhibits left-handed property in two frequency detuning bands of the probe field. The real and imaginary parts of the refractive index have negative values in the same frequency band. We can use this atomic system as an active medium for amplification of electromagnetic fields. In the absence of the SGC effect, we can easily control the transition between the OB and the OM effects by modifying the sign of the refractive index. In the presence of the SGC effect, we observe the OM behavior in this system such that the threshold of the OM in the negative refractive index band is less than the positive refractive index band. In this system, the negative refractive index, the OB and the OM behaviors can be controlled based on the effect of quantum coherence.